This invention relates to semiconductor devices and in particular, to bipolar semiconductor devices and means of stabilizing same.
High frequency bipolar transistors, such as those typically used with Emitter Coupled Logic (ECL) circuits, have a tendency of being conditionally stable. Measurements have shown that this conditional stability appears as a negative real part of the input impedance which can cause undesirable oscillations. One solution to this problem is the addition of a resistor in series with the base to cancel the negative resistance and thereby increase stability. This solution can significantly increase the response time of the transistor. Other solutions are to increase the collector resistance, which adversely affects response time, or to significantly increase the collector-base capacitance, which also adversely affects response time. Another solution is to add the series combination of a resistor and transistor between the base and collector of the transistor whose operation is to be stabilized. This solution is very expensive in terms of the added silicon area needed for the implementation thereof.
It would be desirable to be able to compensate for transistor instability without significantly affecting transistor response time, fanout capability, or the physical size of the transistor structure.